As an organic light-emitting device, a device with a multi-layered structure having a light-emitting layer containing a phosphorescent low-molecular weight compound between a hole transport layer and an electron transport layer has been known.
On the other hand, a phosphorescent polymer compound that is obtained by copolymerizing a polymerizable compound having a phosphorescent property, a polymerizable compound having a hole transport property, and a polymerizable compound having an electron transport property has also been developed. Such phosphorescent polymer compound has a merit of obtaining an organic light-emitting device by merely providing one layer comprising this polymer compound, since it has the functions of the hole transport property and the electron transport property as well as the phosphorescent property within a single compound.
In the past, for the synthesis of the polymer compound, polymerizable compounds have been used, wherein polymerizable substituents were introduced into each of publicly known phosphorescent low-molecular weight compounds, low-molecular weight compounds having hole transport property, and low-molecular weight compounds having electron transport property (see patent documents 1 and 2).
In this manner, however, when a phosphorescent low-molecular weight compound that is preferably used for the multi-layered devices is copolymerized with a polymerizable compound having a hole transport property and a polymerizable compound having an electron transport property, the device having a tendency to deteriorate more easily than the multi-layered devices may be obtained in some cases.
Also, in the polymer compound described above, it was difficult to attain high luminous efficiency by efficiently generating excitons on the structural unit having the phosphorescent property. This is because, in a polymer compound having all functions in a single layer, it is necessary to combine the energy levels of each compound having the phosphorescent property, the hole transport property and the electron transport property more strictly than the case where the multi-layered device was prepared, thus the selection of each compound is very difficult.
Further, it has been known that when a polymer compound containing a structural unit having the phosphorescent property in high concentration was used in order to improve the luminous efficiency, the concentration quenching took place on the contrary, and as a result, high luminous efficiency was not attained.    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2002-293830    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2003-73479